Electric furnace



0d. 6, C. B. FOLEY ELECTRI C FURNACE Filed March 13, 1920 INVENTOR 5 1 0 454.

EZtw W ATTORNEY Patented Oct. 6, 1925.

UNITED STATES CHARLES .B. FOLEY, OF BRISTOL, CONNECTICUT, ASSIGNOR TO CHARLES OF NEW YORK, N. Y., A

FICE.

B. FOLEY, Inc,

PATENT 0F RPOBA'IION OF NEW YORK.

anaemic rummon.

Application filed larch 13, 1920. Serial No. 385,634.

To allwkomitmag concern:

Be it known that I, CHARLES B. FOLEYLG citizen of the United States, and a resident of Bristol, in the county of Hartford and State of Connecticut, have invented certain new and useful Improvements in Electric Furnaces, of which the following is a specification.

My invention relates to electric furnaces, and my object is to eliminate certain wellknown dilficulties arising in the operation of furnaces of this type by what is known as the pinch efi'ect.

When an electric current. flows in a liquid conductor, the mutual attraction which exists between the current-bearing elements produces a resultant pressure at the axis of the conductor which varies directly as the square of the current and inversely as the cross-section of the conductor. In electric induction furnaces of the ring type, wherein the molten secondar is arranged horizontally and is of uni orm cross-section, this pressure is the same at all axial points of the secondary and hence there is no tendency to the flow of metal along the axis. But if it should happen, for any reason, that the channel is constricted at any point, the axial pressure at that point immediately rises owing to the decreased cross-section of the secondary; and, consequentl the molten metal will move axially from t is point towards contiguous portions of great crosssection and less pressure, producing a further constriction of the secondary and a proportionately greater difference of pres sure. The secondary will, therefore, con tinue to decrease in cross-section until the axial pressure is balanced by the opposing head of metal; or, if the current exceeds a value sufiicient to cause the pressure to exceed the hydrostatic pressure at that point, the secondary will be ruptured, thereby causing injury 'to the furnace structure, vaporization, and oxidation of the metal, and complete interruption in the operation of the furnace. This phenomenon is known as the pinch eflect. It imposes a limit on the secondary current be 0nd which the furnace cannot be operate The same phenomenon occurs in the 0 eration of furnaces of the crucible type, w lierein the heat is created b electric current flowing in a molten con uctor of nonuniform cross-section. In a crucible furnace such as disclosed in my copending application, Serial No. 139,437, the hydraulic head of metal is purposely made high to oppose a high pressure to the pinch forces, so that a relative] high current density may be employed. 1 ave found, however, that even in the crucible furnace of this type, ut lizing a relatively high head of metal, the pinch effect is objectionable, particularly in the specific furnace which I have invented. In my furnace, which is of the inductlon crucible type, the heat is largely generated in a constricted portion of the secondary at the bottom of the furnace. To produce the heat required for melting metal of high conductivity, the current density must be relativelygreat. It is the obect of my invention to lessen the pinch effect so that I ca use the highest possible current density without causing rupture of the secondary. The invention, however, is not limited in its application to any tlcular type of electric furnace, but it is capable of use in an situation where it is desired to lessen the pinch effect.

The method I employ to carry out the object of my invention will be clearly understood from the following description.

In the drawings,

Fig. 1 is a vertical section of a crucible having my invention applied "thereto;

Fig. 2 is a similar section on the line 2-2 of Fig. 1; and

Figs. 3 and 4 are detail views illustrating the principle of the invention.-

I will first explain theprinciples under lying my invention and then describe a furnace embodying said principles. The force giving rise to the pinch effect in liquid conductors through which an electric current flows of the conductor and tending to squeeze it into a smaller cross-section. If the liquid conductor is conceived of as a bundle of individual current-bearing elements, it is readily seen that, just as two or more adjacent parallel conductors carrying currents of the same direction attract one another and tend to move together, so the currentbearing elements of the liquid conductor attract one another and produce a resultant pressure at the central axis of the conductor which varies directly as the current density in the conductor.

I have conceived and reduced to practice paris a force acting transversely channel is divided into current-bearing the idea of decreasing this axial pressure in a liquid conductor carrying an electric current by subjecting said conductor to the neutralizin action of a contiguous conductor in whic an electric current flows in the same direction.

The theo upon which my invention is based will l ie readily understood from a consideration of Figs. 3 and 4.

Fig- 3 represents in cross-section a channel formed of refractory walls and carrying a molten, or fluid, conductor of electricity. The channel is shown subdivided into three sections b longitudinal partitions 5. Assuming t at a current of electricity flows through the fluid conductors, the radiallyactin forces which produce the pinch effect may e represented in a general way by the arrows pointing towards the axes of the sub-conductors. It willbe noted that the forces represented by the arrows at in one conductor are generall opposed by the forces represented by t e arrows b 1n the contiguous conductor That is, the pull on the current-bearing elements in the righthand portion of conductor 1 exerted b the elements in the leftand portion of the same conductor is opposed and partially neutralized by the pull exerted by t e current-bearing elements in the lefthand portion of conductor 2; and, reciprocally, the pull on the current-bearin elements in the left-hand portion of con uctor 2 exerted by the current-bearing elements in the right-hand portion is opposed by the ull exerted by the current-bearing elements in the right-hand portion of conductor 1. It is apparent, therefore, that the forces represented by the arrows a and b of the three conductors are to a large extent nullified, conse uently decreasing the axial ressures of t e individual conductors. his construction, therefore, effects a very considerable reduction in the pressure exerted at the axes of the sub-conductors, producing a corresponding reduction in the pinch effect in addition to the reduction caused by the mere subdivision of the conductor.

Fig. 4 shows a somewhat different embodiment of the same principles. Here, the 5 well-defined sub divisions by longitudinal ribs projecting from the channel walls. generally the direction of the forces brought about by the mutual attraction between the current-bearing elements of the conductor.

In Figs. 1 and 2, I have shown an electric induction furnace embodying my invention. Numeral 6 desi ates a crucible body of refractory material; 7, a tube integral with the side walls of 6, open at both ends and containing the core 8 and winding 9 of a transformer, the secondary of which is formed by the molten metal contained in the crucible. The channel is divided into The arrows show four sections each connecting with the pool of molten metal, as indicated in Figs. 1 and 2, by plates 11,. which may be composed of any suitable refractory material. The plates may be attached in sition in any suitable manner, as by being formed in halves and inserted in complementary slots formed in the lower portion of the crucible and tube 7 and then cemented permanently in place. Or, they may be formed integrally with the furnace structure. The plates 11 not only effect a ver considerable decrease in pinch forces y dividing the constricted part of the secondar into longitudinal sections, but the ad very materially to the mechanica strength of the lower part of the furnace where the stresses produced b the electro-dynamic forces and the hydraulic pressure of the molten metal are greatest.

Another advantage resulting from this form of electric induction furnace arises from some or all of the separated channels being located on one side or the other of a plane extending at right angles to the axis of the primary coil 9 and located midway between the ends of said coil. Such a plane would pass through the middle one of the three partitions 11 shown in Fig. 2 and it is evident that the molten metal of the secondary located, say in the extreme left hand channel 10, will as a result receive a greater thrust to the left from the repulsion action of the primary current than toward the right. This will tend to drive the molten metal in said channel toward the left handwall thereof and out of the left hand side of each terminal of said channel into the pool above, thus creating a counter inflowing current at the right hand side of said channel to fill the vacuum tending to be formed by the above described outflow. This accelerates the circulation of the molten metal in the furnace and tends to distribute the heat throughout the molten mass more rapidly, which is a highly desirable result. In the same way a thrust to the right side of the extreme right hand channel would be exerted on the metal in it, and with the same result in accelerated circulation above described.

Having fully described my invention, I claim:

1. In an electric furnace, a channel formed of refractory material and ada ted to contain metal in the molten state, ongitudinal partitions subdividing the channel into a' plurality of sections, whereby the pinch effect, caused by a current of electricity in the metal, is lessened.

2. In an electric furnace, a channel adapted to contain molten metal carrying electric current, said channel being subdivided longitudinally to lessen the pinch effect.

3. An electric furnace of the crucible type adapted to contain a pool of molten metal,

channels communicating with the pool near the bottom thereof, and means for longitudinally dividing the channels to decrease pinch effect.

4. An electric furnace comprising a body of refractory material adapted to hold a pool of molten metal and having walls forming a restricted channel communicating with the pool, longitudinal ribs projecting 'from the channel walls and cooperating to produce subdivisions of the channel.

5. The method of lessening the pinch effect caused by the flow of an electric current through a liquid conductor, whiclrconsists in subdividing the conductor into a plurality of closely adjacent sections whereby the opposing radially-acting electromagnetic forces of ad acent portions of the conductors are substantially neutralized.

6. An electric furnace of the crucible type adapted to contain a pool of molten metal carrying electric current, means to form a portion of the molten metal into a channel for circulating purposes having its smallest crosssection at the bottom of the furnace and gradually increasing in cross-section as it meets the metal of the pool, a transformer device to produce current in the channel, and means for longitudinally dividing the channel effectively along its restricted por tion to decrease the pinch effect.

7. An electric furnace of the crucible type adapted to contain a pool of molten metal carrying electric current, means to form a portion of. the molten metal into a channel for circulating purposes havin its smallest cross-section at the bottom 0 the furnace and gradually increasing in cross-section as it meets the metal of the pool, a transformer device to produce current in the channel, and means consisting of partitions" extending completely across the circulating channel for longitudinally dividing said channel along its restricted portion to decrease the pinch effect.

8. An electric furnace comprising a receptacle having a channel of loo form opening into the interior thereof t rough flaring mouths, said receptacle having an opening formed within the channel loop, a primary winding located in the opening with its axis transverse to the plane of the loop, and means for longitudinally dividing the channel to decrease the pinch efiect.

9. An electric furnace having a channel of loop form opening into the interior thereof, said furnace having a transverse opening therethrough within the channel loop, and a primary winding and core within the opening, said channel having an elongated cross-section with its major axis substantially parallel with the axis of said primary winding, and means for longitudinally subdividing the channel to decrease the pinch effect.

10. An electric furnace, comprising a receptacle having a channel of loop form with flaring mouths opening upwardly into the interior thereof, the outer periphery of the channel being continuous with the interior wall of the receptacle, said receptacle having an opening formed therethrough within the channel loop, and means for longitudinally dividing the channel effectively to decrease the pinch effect.

11. An electric furnace of the crucible type comprising a receptacle adapted to hold a pool of molten metal, said receptacle having interior walls forming a plurality of substantially parallel channels opening upwardly into the interior of the receptacle at opposite sides thereof.

12. An electric furnace comprising a receptacle adapted to hold a pool of molten metal, said receptacle having interior walls adapted to form a portion of the molten metal into a plurality of loops depending from the bottom of the pool.

13. In an electric furnace the combination of a container for a pool of molten metal and a looped channel formed of refractory material below the same arranged in a substantially vertical plane and adapted to contain metal in the molten state, and a primary coil, the axis of which coil is substantially horizontal and perpendicular to the plane of said loop, the central plane of said looped channel being located to one side of a parallel plane passing through the primary coil at a point midway between the ends of said coil.

CHARLES B. FOLEY. 

